Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
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Hi, glad to be of help. This sounds to me it is a bad connection to/from or bad ignition module or coil pack. A bad cam sensor will affect injector pulse. You may also have a bad reluctor wheel for the crank sensor but not probable. Being that you are not getting a tach signal, the problem lies in this area. Check injector pulse with a noid light and check at coil negative for a flash pulse while cranking. If you are getting injector pulse the problem is not cam sensor. If you are not getting or intermittent flash pulse at coil negative while cranking, the problem is ignition module or crank sensor. If you are getting steady flash pulse, the problem is coil pack. If you are not getting injector pulse, the problem is cam sensor or ECM. If you are getting flash pulse at coil negative and no injector pulse, the problem is ECM.
Symptoms of a bad camshaft
Typically popping through the carb is a tell tale sign. Loud rockers (tapping is a sign).
popping through the exhaust is also a sign. If a lobe went flat then you would have lifter, push rod, and rocker clacking pretty good. 1st symptom is you have a faint tap and need to adjust the tappet. Put a vacuum gauge on the motor some where and see if there is fluctuation in the needle if there is very possible cam problem. You can pull the valve covers and crank it and see which, if any, rockers don't move or only move slightly. Backfiring through the carb, increasing rocker noise(single), and from memory, all this goes from noticeable to real bad in about 50 miles.
There are two different coil pack set ups and not sure which one you have, but ignition module is directly underneath the coil pack. The magnavox type coil pack is one unit, the other type is individual, usually one coil per two cylinders. If you have indiviual coils for each and every cylinder, you are correct, the ECM performs all the fucntions and there is no ignition module. Crank sensor relates to spark at the plugs and cam sensor relates to fuel injectors firing.
Get a noid light to check injector pulse. It looks like this:
They make different ones for different applications. You can get a noid light set here or at any auto parts store or Sears.
I just checked on your system and you have individual coils, one on each cylinder and you are correct, the PCM does it all. You need to check your circuits. Here are the diagrams:
Cam & crank sensor circuit diagram
If your circuits check out, replace the ECM.
Here's some videos for testing your cam & crank sensor circuits:
Crank sensor circuit testing
Cam sensor circuit testing
Cam & crank sensor testing
The symptom of a bad cam sensor is no injector pulse.
need help on a 1999 Chevy K3500 pickup with a 7.4 L